The present invention relates to a method of and apparatus for wrapping large objects. More particularly this invention concerns a system for wrapping palletized freight with a shrinkable film.
A standard freight-wrapping apparatus has a portal frame, a conveyor extending through the portal frame and having a stretch supporting the package, driven foil-supply rolls whose foils are connected at their ends to form a curtain extending across the portal, and double-weld beams movable together from opposite sides of the portal. The package to be wrapped is conveyed through the portal frame to entrain the curtain so that same wraps around it whereupon the double-weld beams move together to weld the foils together behind the package. It is standard for such an apparatus to use stretch or shrink foils that are then heated to secure them tightly about the package.
A disadvantage of this system is that when the welding beams are moved together to draw the curtain foils together they create additional tension in the foils. This tension can displace the package and/or overstretch the foils. In particular when the package is a stack of cartons stacked on a pallet, the tension in the foil can upset the stack.
It is therefore an object of the present invention to provide an improved system for wrapping large objects.
Another object is the provision of such an improved system for wrapping large objects which overcomes the above-given disadvantages, that is which wraps the packages without over-tensioning the wrapping material.
A package is wrapped with foil by forming a curtain of two foils pulled from respective supplies with the curtain extending transversely across a conveyor path at a wrapping station and displacing a package to be wrapped in a forward transport direction along the path into engagement with the curtain and through the station so that the foils extend downstream past the package. Then a pair of double-weld beams are moved together on opposite sides of the foils downstream of the station to press and weld the foils together downstream of the package while at the same time the package and beams are relatively displaced in the direction toward each other as the beams are moved together to reduce tension in the foils created by inward movement of the beams.
Thus with this system the beams are moved downstream or the package is moved upstream in order to prevent the inwardly moving beams from tensioning the foils so much that they break or displace the package. The relative movement in the transport direction takes place during the second half of the movement together of the weld beams, when most tension would be put in the foils. This system ensures that when the package is formed of a stack of even relatively light objects on a pallet, they will not be shifted when wrapped.
The beams according to the invention extend vertically and are displaced transversely of the direction when moved inward toward each other. In addition the beams form a pair of horizontally spaced weld seams in the foils between which the foils are cut to free the package and form a new curtain extending crosswise across the path.
The conveyor can be made with support arms or the like engaging into spaces so that the exterior surfaces of the package are freely accessible for wrapping the package.
The wrapping apparatus according to the invention has a portal frame at a wrapping station, a pair of foil supplies on the frame, feed and looper units associated with the foil supplies for forming a curtain of two foils pulled from the supplies with the curtain extending transversely across the portal frame at a wrapping station. A belt, chain, or beam-type conveyor displaces a package to be wrapped in a forward transport direction along a path extending through the portal frame into engagement with the curtain and through the station so that the foils extend downstream past the package. A pair of double-weld beams at the station are movable transversely of the direction toward and away from each other by a controller. Thus the beams are moved together on opposite sides of the foils downstream of the station to press and weld the foils together downstream of the package while relatively displacing the package and beams in the direction toward each other as the beams are moved together to reduce tension in the foils created by inward movement of the beams.
The controller can displace the package upstream, that is backward in the direction, relative to the beams during movement together of the beams, or can move the beams downstream, that is forward in the direction, to achieve the desired de-tensioning effect. The path according to the invention is horizontal. It could also be vertical with the portal oriented horizontally.
The controller includes a sensor for determining the position of the package relative to the frame. Furthermore the supplies are rolls having center axes and the frame has supports holding the rolls with their axes horizontal. Respective elements deflect the foils into a vertical orientation in the curtain. Respective loopers between the supplies and the curtain, and drive continuously pull the foils from the respective supplies. Thus on changing of the foil rolls a stacker or a hand lift truck can be used since they are delivered on a pallet and are lifted into the apparatus. As a result the expense of handling and likelihood of an accident during changing the foil rolls is reduced. Bearings are provided outside the frame for the axes of the foil rolls.
Here electronic control of the rotation rate of the drives to accommodate the foil as it is used can be eliminated. The rotation rates of the drives is not determined by the instantaneous movements of the apparatus or the transport speed of the packages since the loopers can be constantly refilled and emptied as needed. To this end the foil loopers each have at least one dancer roller.
It is also possible to mount several foil rolls on at least one side of the frame. Thus one foil roll can be a supply roll that is put into service when the other roller is used up. This reduces the down times during foil change. It is also possible to use foil rolls with different foils that can be used as needed. When space is limited the foil rolls can be mounted on one side. In this case the foil is guided from one side over the apparatus.
The system for sensing movement of the double-weld beam can be a rotary pulse generator, an angle detector, or the like for controlling the foil-roll drives so that the drive speed of the foil rolls can be adjusted in dependence on the movement of the arms of the foil supports and deflecting rolls.